The purpose of this research is to define biochemical mechanisms important in the control of gene expression, and to discover how these mechanisms may be altered to regulate male fertility. In particular, the hormone-dependent differentiation of rat testis cells will be utilized as a model system. In this animal the process of development from spermatogonia to spermatozoa proceeds in a highly synchronized pattern from birth to maturity, and sequential steps in development in the tissue can be analyzed according to a precise chronological format. Alterations in gene expression are marked by the initiation or termination of synthesis of specific proteins. Knowledge concerning these biochemical regulatory factors will then be applied to studies of human testis and sperm. The results will lead to a definition of male infertility syndromes in terms of specific defects in the molecular biology of testis cells. Elucidation of the many complex biochemical mechanisms which govern spermatogenesis may provide the basis for pharmacological regulation of male fertility.